Various capacitive structures are used as electronic elements in integrated circuits such as radio frequency integrated circuits (RFIC), and monolithic microwave integrated circuits (MMIC). Such capacitive structures include, for example, metal-oxide-semiconductor (MOS) capacitors, p-n junction capacitors and metal-insulator-metal (MIM) capacitors. For some applications, MIM capacitors can provide certain advantages over MOS and p-n junction capacitors because the frequency characteristics of MOS and p-n junction capacitors may be restricted as a result of depletion layers that form in the semiconductor electrodes. A MIM capacitor can exhibit improved frequency and temperature characteristics. Furthermore, MIM capacitors are formed in the metal interconnect layers, thereby reducing CMOS transistor process integration interactions or complications.
A MIM capacitor typically includes an insulating layer, such as a PECVD dielectric, disposed between lower and upper electrodes or plates. To reduce the cost, thinner metal plates are highly desirable. Thin metal plates, however, can cause degraded performance. Namely, the MIM capacitor quality factor can be degraded due to current crowding within the thin metal. Typical square or rectangular MIM capacitors exacerbate this problem due to the length that the current has to travel through the thin metal. For example, in a conventional MIM capacitor with a bottom plate (M1), a middle plate (M2) thinner than the bottom plate, and a top plate (M3) thicker than the bottom plate (M1) to ensure dielectric integrity, the bottom plate (M1) surface can become highly irregular if bottom plate (M1) thickness grows too much, causing MIM breakdown voltage to be lower and variation to increase. The bottom plate (M1) has much higher resistance than top plate (M3) causing bottom plate (M1) to become and RF Q-factor bottleneck. Thus, there is a need to reduce the effective bottom plate (M1) resistance through process or design changes to avoid the MIM capacitor quality factor from being degraded due to current crowding within the thin bottom plate (M1). However, these changes are expensive and physically limited.
Accordingly, there is a need for systems, apparatus, and methods that improve upon conventional approaches including the improved methods, system and apparatus provided hereby.